As energy source prices are increasing due to depletion of fossil fuels and interest in environmental pollution is escalating, demand for environmentally-friendly alternative energy sources is bound to play an increasing role in future. Thus, research into various power generation techniques such as nuclear energy, solar energy, wind energy, tidal power, and the like, is underway, and power storage devices for more efficient use of the generated energy are also drawing much attention.
In particular, demand for lithium secondary batteries is rapidly increasing as mobile device technology continues to develop and demand therefor continues to increase. Recently, lithium secondary batteries as a power source of electric vehicles (EVs) and hybrid electric vehicles (HEVs) are used and the market for lithium secondary batteries continues to expand to applications such as auxiliary power supplies through smart-grid technology.
Generally, lithium secondary batteries have a structure in which an electrode assembly, which is impregnated with a lithium electrolyte, including a cathode including a lithium transition metal oxide as an electrode active material, an anode including a carbon-based active material, and a porous separator. A cathode is manufactured by coating a cathode mixture including a lithium transition metal oxide on an Al foil. An anode is manufactured by coating an anode mixture including a carbon-based active material on a Cu foil.
To improve electrical conductivity, a conductive material is added to a cathode mixture and anode mixture. In particular, a lithium transition metal oxide used as a cathode active material has low electrical conductivity and thereby, a conductive material must be added to a cathode mixture. Among conductive materials, conventional conductive materials used in order to improve conductivity of a cathode mixture have a drawback that loading density could not be enlarged at a compression process reducing thickness of a cathode mixture.
Therefore, the need for new technologies which improve performance of secondary batteries by using new conductive materials which may substitute for conventionally used carbon black, graphite and the like is very high.